The present invention is directed generally to electrical connectors of a type providing protection from electromagnetic interference (EMI). More particularly, the invention is directed to a multiple contact filter connector capable of conducting high RF currents and a method of fabricating the same at greatly reduced manufacturing cost.
In numerous applications, such as where long unshielded cable runs enter a shielded housing containing circuitry sensitive to extraneous signals picked up by the cable, it is necessary to provide electrical filter networks as an integral part of a connector to suppress transients and other undesired signals, such as EMI, which may otherwise exist on circuits interconnected by the connector. An illustrative prior art filter connector used in such applications is shown and described in Tuchto et al, U.S. Pat. No. 3,854,107 and pending Boutros U.S. patent application Ser. No. 875,363, filed Feb. 6, 1978 and now U.S. Pat. No. 4,195,272, both assigned to the same assignee as the present invention.
The filter connector illustrated in the aforementioned Tuchto et al patent includes a dielectric body supporting a plurality of filter contacts and a thin conductive foil ground plate. Each filter contact includes a filter network comprising multiple concentric filter elements coaxially mounted on a reduced diameter portion of the contact and an outer ground electrode. The filter contacts are dimensioned and configured to accommodate insertion and removal from the dielectric body with the ground electrodes contacting the thin foil ground plate in a wiping action.
While multiple contact filter connectors of the foregoing variety have proven successful when used to conduct relatively low RF currents of approximately one-quarter ampere, they have not been suitable for conducting high RF currents of, for example, three or more amperes. Because the ground plates are thin, and the surface contact with the filter elements necessarily limited the heat generated by high current conduction cannot be adequately dissipated. As a result, the connectors overheat and, ultimately, fail.
In order to overcome this problem some prior art connectors employ a relatively wide metal ground plate. While such wide metal plates have sufficient mass and conductivity to dissipate the extreme heat generated by high RF current conduction, they are not flexible and, as a result, are not suitable for making low resistance wiping contact with the surface of the network filter ground electrodes. Hence, other means must be provided for establishing the required electrical connection between the ground plate and the network filter ground electrodes. In some prior art connectors the network ground electrode, and therefore the filter itself, is conductively bonded to the ground plate with a conductive adhesive, such as conductive epoxy. This approach, however, engenders other disadvantages. For example, each ground electrode must be individually bonded to the ground plate. Typically, a single connector may include as many as 120 network filters, and as a result, the manufacturing costs in fabricating such a connector in this manner is extremely high. In addition, after fabrication, should one of the network filters be found to be defective, in most cases, the entire connector must be discarded since replacement of the faulty network filter is usually not possible. Moreover, removal of the faulty network filter, if possible, would jeopardize the bond between the ground plate and the other network filters. One suggested solution to this problem is to test each individual network filter prior to its placement and bonding within the connector. But even this approach fails to provide a complete answer because there is always the possibility that one or more of these fragile filters might be damaged during network filter installation and bonding within the connector.
A number of the above considerations have ben addressed in the referenced U.S. patent application Ser. No. 875,363 wherein conductive epoxy is employed in a connector to form a common grounding plate in electrical connection with a plurality of tubular capacitors which function as contact filters. Such construction is capable of dissipating heat at rates as considered herein. Epoxy grounding plates as considered in Ser. No. 875,363 have been bonded directly to encapsulating connector housings or have been electrically connected to the housings by intermediate grounding springs, but it has been recognized that improved conductivity between the grounding plates and housings would be desirable.